JPS5824905B2 - radiation detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radiation detector, and particularly to a radiation detector that is used to expose a subject to be examined (for example, a human body) from all directions to collimated radiation (X-rays or gamma rays) in a pencil or fan shape. CT (Computerized CT) reconstructs a tomographic image in the direction of radiation transmission by detecting the transmitted radiation with a detector, measuring the absorption rate of the radiation in the subject, and performing appropriate processing on a computer. Tomograp
Suitable for high scanners.

This relates to a radiation detector.

Electromagnetic radiation or radiation in the X-ray frequency range (hereinafter referred to as X
gaseous media of a type characterized as substantially opaque (xenon, krypton,
Conventionally, an ionization chamber or a proportional counter tube is used to efficiently collect ion pairs obtained by the interaction between X-rays and the gaseous medium by sealing argon (argon, etc.) in a pressure vessel 3 at high pressure as shown in Figure 1. More suggested.

X-rays enter the pressure vessel 3 from the direction of arrow 1 through an entrance window 2 made of a material through which X-rays can easily pass, such as aluminum, plastic, or beryllium.

A high atomic weight gas is sealed in the pressure vessel 3 under high pressure, and X-ray photons interact with this gas in the presence of an electric field to produce photoelectron-ion pairs.

This electric field is created by a high voltage electrode 4 and a signal electrode 5 made of a thin metal wire.

A molybdenum or tungsten wire with a diameter of about 10 to 100 microns is used for the signal electrode 5, and the high voltage electrode 4
Enables the application of a strong electric field between the

Electrons and positive ions generated by the interaction between the X-ray photons and the gas flow along the electric field, causing avalanche collapse of the gas near the signal electrode 5.

That is, a detector characterized as a multilinear proportional counter is configured.

The signal amplified by this gas avalanche phenomenon (also referred to as gas amplification effect) is taken out from the signal line 6 through the terminal I to the outside of the pressure vessel.

The terminal T is made of a highly insulating material such as ceramic or epoxy resin, so that it is insulated from the pressure vessel 3 and is designed to prevent high-pressure residue from getting wet.

FIG. 2 is a longitudinal cross-sectional view of the electrode portion of FIG. 1 taken along the X-ray incident direction.

By the way, in such a conventional X-ray detector, ion pairs are converted into ion pairs in the region sensitive to X-rays, that is, the region surrounded by the high-voltage electrode 4 (hereinafter referred to as the sensitive region), and are extracted as an electrical signal from the signal electrode 5. The X-rays generated are only about 60% of the incident X-rays, and the remaining 40% passes through the sensitive area and reaches the bottom of the pressure vessel.
0, resulting in scattered X-rays 9.

Since the scattered X-rays 9 from the pressure vessel bottom 10 are generated regardless of the incident direction, other adjacent electrode limiting chambers (adjacent detection elements)
Since the X-rays stray up to the point where they are detected in the same way as the incident X-rays, the spatial resolution of such multi-channel detectors deteriorates, which in turn causes a decline in the diagnostic ability of tomography.

It is an object of the present invention to provide a radiation detector that is improved from the above-mentioned drawbacks.

In the present invention, as described above, it is possible to effectively utilize up to 40 times of incident X-rays that pass through the sensitive area, and to prevent a decrease in spatial resolution.

FIG. 3 is a perspective view showing a typical electrode structure of the first embodiment of the present invention, and FIG. 4 is a sectional view for explaining its operation.

In the present invention, as shown in the same figure, the high voltage electrode 4 and the signal electrode 5 themselves are the same as the conventional ones, but a radiation blocking plate 11 formed of heavy metal is added at the bottom of the high voltage electrode 4, that is, at the bottom of the sensitive area. is installed.

Structurally, this blocking plate 11 is formed to have a built-in signal electrode and close the space between adjacent high-voltage electrodes 4, and preferably has the same voltage potential as the high-voltage electrodes.

The radiation blocking plate 11 is preferably made of a material such as tungsten, lead, or molybdenum that easily emits fluorescent X-rays when X-rays are incident thereon and has a high X-ray blocking ability.

Next, the operation of this detector will be explained.

The incident X-ray 1 operates in exactly the same way as a conventional detector until it reaches the blocking plate 11.

Sensitive part consisting of tp high voltage electrode 4 and signal electrode 5 (
The gas in the electric field (with φ ℃・ru) is ionized by the photoelectric effect, Compton effect, etc., and ions/phantoms are generated.

The generated electrons and positive ions flow along the electric field and reach the signal electrode 5.
The gas is amplified by the high electric field near , and flows into the signal electrode 5 .

40% of the incident X-rays 1 that pass through this sensitive part as described above impinge on the radiation blocking plate 11 and are absorbed, or emit characteristic X-rays (fluorescent X-rays) etc. specific to the material of the blocking plate. death,
A part of the absorbed energy enters the sensitive part again as scattered X-rays.

If the energy of the incident photon is 80 KeV, if the blocking plate 11 is made of lead, the 98th fraction of the X-rays passing through the sensitive region will be stopped at about 0.5 mm.

Now, due to the interaction between this X-ray and the blocking plate 11, the blocking plate 1
1 generates fluorescent X-rays (due to the transition of lead shell electrons), and a portion of the generated X-rays becomes scattered X-rays 9 and enters the sensitive portion again to generate a signal.

The signal due to the scattered X-rays 9 only enters the detection element into which the X-ray 1 has entered, and does not enter into adjacent detection elements and reduce the spatial resolution.

Furthermore, if the high-voltage electrode 4 is made of heavy metal such as tungsten or molybdenum, there will be no problem with reduction in spatial resolution due to crosstalk.

These scattered X-rays 9 are about 15 times the amount of incident X-rays that have passed through the air, but since these X-rays can be used as signals again, overall the efficiency of the detector has been improved by several orders of magnitude. It turns out.

The present invention is as described above, and has the effect of not only improving spatial resolution but also improving sensitivity.

[Brief explanation of the drawing]

Figure 1 is a perspective view showing the configuration of a conventional radiation detector; Figure 2 is a perspective view showing the configuration of a conventional radiation detector;
3 is a sectional view of the main part of the first embodiment of the present invention, and FIG. 4 is a sectional view of the electrode portion shown in FIG. 3 for explaining the operation. １・・・・・・・・・Incoming radiation, ４・・・・・・・・・
・High voltage electrode, 5... Signal electrode, 11...
・・・・・・Radiation blocking plate.

Claims (1)

[Claims] 1. A signal electrode formed of a thin metal wire, a high-voltage electrode provided opposite to this signal electrode, and an adjacent electrode provided at right angles to the incident direction at the end opposite to the radiation incident side of this high-voltage electrode and containing a built-in signal electrode. A radiation detector in which a radiation blocking plate made of heavy metal that closes the gap between high-voltage electrode plates is sealed in gas.